1. Field of the Invention
The subject matter of the claimed invention is a composite article of manufacture from which a number of low friction devices are adapted to be made in duplicate. Each such device is adapted to be fixed in a housing to provide a bearing surface and comprises a sleeve, bushing or liner of a filament reinforced resin material having a low friction bearing surface. Class 160.
2. Description of the Prior Art
The prior art includes the molding of bearings or bearing liners directly over the journal or a mandrel substitute therefor; the manufacture of a series of bearings in the form of a tube which is then cut into short lengths; winding resin-bound glass-filament tapes over a long mandrel in the manufacture of reinforced plastic pipe; and braiding yarns of low friction material on a long mandrel and thereover braiding glass-filaments to form a resin-bound tubular structure which is then cut to bearing lengths.
The low friction characteristics of various polyethelenes has also been known since, for example, publication of British patent No. 698,611. As described therein, the polyethelene is drawn into filaments and woven with other yarn into a cloth which is embedded in a resin which is then hardened to comprise the bearing.
An equivalent of polyethylene developed and sold as "Teflon" by E. I. du Pont de Nemours and Company, Wilmington, Delaware has outstanding low friction characteristics when drawn into a filament. Teflon is a tetrafluoroethylene which is stable and heat and wear-resistant. However, this material is difficult to use because it is subject to cold flow under pressure and the few hardenable plastics or liquids which will adhere securely thereto are themselves difficult to handle.
U.S. Pat. No. 2,885,248 discloses a method of overcoming the cold flow difficulty by eliminating the "other yarn", i.e. by making the exposed cloth entirely out of Teflon so that the unexposed Teflon is entirely surrounded only by the hardened material in which it is embedded.
U.S. Pat. Nos. 2,804,886 (Re. 24,765) discloses a method of overcoming the bonding difficulty by providing a "compound" cloth woven so that the Teflon threads substantially form the exposed bearing face and leave the bondable yarn to form the other or opposite side.
The manufacture of bearings as taught by these patents requires that such cloth and the resin be placed under heat and pressure between the assembled bearing parts to be sure that the fabric is embedded in the resin and the resin fills the fabric. This requires that the fabric be cut in swatches, treated with resin, assembled and the assemblies individually handled throughout the entire manufacturing process.
In the prior art type of winding referred to which is adapted to the present invention, roves of glass filaments are drawn from creels under equal tension and passed through a container of liquid resin. The impregnated roves are gathered to form a tape which is wound in spiral layers over a rotating mandrel. Each spiral is pitched or has a pitch angle so that its adjacent turns are spaced a distance equal to or just slightly less than the width of the tape or a multiple thereof.
For example, a multiple of two may be used and the winding may start at the left end of the mandrel. At the right end the direction of the spiral is reversed. At this point, if the pitch angle is too great, the end of the first spiral must be secured to the mandrel to prevent being unwound by the start of the second spiral. This involves stopping the rotation of the mandrel, considerable lost time and extreme inconvenience caused by dripping of the liquid resin of the tape.
On this account, the pitch angle must be something less than 40.degree. so that the tape stays in place when the direction of the winding is reversed. Thus, the mandrel may rotate continuously as the direction of the spiral is reversed at each end thereof.
In this manner the second spiral is crossed over the first; the third spiral is crossed over the second and alongside the exposed parts of the first; the fourth spiral is similarly crossed over the third alongside the exposed parts of the second; the fifth spiral completes the spiral pattern in one direction; and the sixth spiral completes the spiral pattern in the other direction.
Although the enlarged ends of the completed tube where the windings reverse must be cut off and scrapped, this type of winding especially allows high-speed, mass production techniques and is used in the manufacture of reinforced plastic pipe. The present invention successfully utilizes such techniques.